Metal-organic frameworks (MOFs) are a class of new materials well known for their high surface area and pore size. They can be tuned by dictating the various derivatives of amino acids. Most of the reported MOFs in the literature, numbering nearly 25000 till date, are insoluble in water. The brittle nature of these crystalline materials put many challenges for their industrial processing. Further, it is also a challenge to synthesize them in combination with other functional materials without pore blocking and/or decrease of the inner surface area.
Research on Metal-Organic Frameworks (MOFs) has picked up researchers attention because of their diverse topological architectures and applications like gas sorption, catalysis, magnetism and electrical conductivity. Proton (ion) conductivity in solid-state materials are important due to their application in transport dynamics; electrochemical devices, fuel cells and most importantly to understand the complex biological ion channels. For such diverse applications there is a need for the MOFs to have adequate stability in environments that vary in temperature, pressure, water content and such like. A very limited attempt on the proton conductivity on MOFs has been reported where either lattice backbone, added guest molecules like imidazole and 1,2,4-triazole in an anhydrous medium, or water chains and clusters already present inside the framework facilitate proton conduction.
References may be made to Journal J. Am. Chem. Soc. 2009, 131, 13516 by Kitagawa et al. have extensively studied proton conductivity in various MOFs where coordinated water or guest molecules play a vital role in proton conduction. However, the role of halogens (especially halogens coordinated to metals) in controlling proton conduction in MOFs has not been explored at all. Moreover, most of the MOFs, due to their insoluble nature in water can't be fabricated easily as a thin film and usable for proton conduction and various separation applications.
References may be made to Journal entitled “Helical Water Chain Mediated Proton Conductivity in Homochiral Metal_Organic Frameworks with Unprecedented Zeolitic unh-Topology” (JACS) by Sahoo et al which discloses Four new homochiral metal_organic framework (MOF) isomers, [Zn(l-LCl)/(Cl)](H2O)2 (1), [Zn(l-LBr)(Br)]—(H2O)2 (2), [Zn(d-LCl)(Cl)](H2O)2 (3), and [Zn(d-LBr)—(Br)](H2O)2 (4) [L=3-methyl-2-(pyridin-4-ylmethylamino)-butanoic acid], have been synthesized by using a derivative of LID-valine and Zn(CH3COO)2 3 2H2O. A three-periodic lattice with a parallel 1D helical channel was formed along the crystallographic c-axis.
Present invention disclose amino acid based MOFs as a water soluble MOF for industrial application like thin film fabrication etc. which are non-obvious from the point of view that although more than 25000 MOFs have been reported in the literature in the last decade, still most of them are water unstable and thus inappropriate for application in day to day purpose, which narrow down the picture many fold to a few class of MOFs which are water stable. Furthermore, the MOF backbone disintegrates as ligand and corresponding metal oxide/hydroxide by means of which the process become irreversible to reconstruct the MOF. Hence, it will be utmost difficult for a researcher to envisage a homochiral MOF material to be water soluble, which is the most non-obviousness disclosed in the patent. Synthesis of four valine based MOFs in the JACS paper, along with the proton conducting data has been reported. However, the process of water solubility has not been at all discussed anywhere in the paper, which is the most striking feature, as well as the most non-obvious, too. Moreover, in the present patent control over the anion to tune the solubility along with the proton conductivity has achieved. Also, change of the ligand backbone (from valine to alanine) has been achieved to prove the extension of the concept described in the disclosure, which has not been ever discussed in the ma paper. The synthesis of Alanine based MOFs were achieved entirely different procedure described in the JACS paper, as general/straightforward synthetic pathway didn't yield the same. The synthesis of the MOFs with suitable variation of eight synthetic parameters i.e. the ligand backbone, the synthesis temperature, the solvents and their ratio for synthesis, the choice of anion, the reactant ratio and the metal salt as well as the pH of the medium has been reported in the present patent proposal. Hence, under this circumstance we, enable us to claim that any researcher, established and expertise in the synthesis of MOF arena won't be able to synthesize the aforementioned MOFs as now the difficulty level of synthesis has increased eight fold as compared to procedure reported in our JACS paper. Also, the water solubility in non-obvious from the point of view that most of the well known MOFs reported in the literature are water unstable and also they decompose in contact of water. The water solubility information is not reported in JACS paper and also non-obvious for any reader or researcher to envisage the water solubility from the data reported therein. Hence, we have pinpointed the non-obviousness of the process in an elaborated manner along with the new Alanine based MOF structures prepared by suitably adjusting synthesis parameters resulted from the point to point description given in the patent disclosure.
Thus it will highly desirable to have MOFs that have properties that are enlisted herein, but till date, there is no patent or publication available that disclose a MOF with solubility in water. MOFs known in the art, due to their 3-D orientation are known to be water insoluble.
There is therefore a need in the art to provide stable and water soluble MOFs that can be easily fabricated for proton conduction and for various thin film applications.